Method of hobbing blanks



- May 19, 1925.

E. WILDHABER METHOD OF HOBBING BLANKS v Fildb. so, 1922 s Sheets-Sheet 1May 19, 1925.

E. WILDHABER METHOD OF HOBBING BLANKS 5 Sheets- Sheet 2 Fildbc. :50,1922 May 19, 1925. 1,538,773

E. WILDHABER METHOD OF HOBBING BLANKS ild'n. 30, 1922 3 Sheets-Sheet sPatented May 19, 1925.

UNITED STATES:

1,538,773 PATENT OFFICE ERNEST wrrnmuma, or BROOKLYN, NEW YORK, .assienoa 'ro NILES-BEMENT-POND COMPANY, or new YOR-K,'N.' Y.,- aCORPORATION or NEW messy.

'mn'rnon' or HOBBING nnanxs.

. Application filed December 30, 192 2. Serial No. 609,944.

To all whom itmag concern Be it known that I, ERNEST WILDHABER, acitizen of the Republic. of Switzerland, residing at Brooklyn, in thecounty of -Kings and State of New York, have invented certain new anduseful Improvements in Methods of Hobbing Blanks, of' which thefollowing is a specification.

My invention relates to methods of hobbing sprocket wheels ofthe silentchain type, spline shafts, and similar articles having teeth providedwith straight profiles.

,One object of my invention is to provide a method of forming a sprocketwheel from a blank that shell consist in providing a hob having twofinishing cutting edges located on different hob teeth, in positioningthe hob with respect to the blank so that the opposite sides of adjacenttooth spaces are simultaneously finished, and in efiectin relativerotation blank.

Another object of my invention is to pro between the hob and the ride amethod of forming a sprocket wheel from a blank that shall consist inproviding a hob having form cutting edges, and inoperating the hob andblank with respect to each other whereby the hobwill out teeth to fit apredetermined chain irrespective'of the number of teeth on the blank.

Another object of my invention'is to provide a method of forming asprocket Wheel or a spline -shaft from a 'blankthat shall consistin'providing a hob having teeth arranged in the form of a. thread with adifferent lead on opposite sides of the teeth,

in positioning the hob relative to the blank so that two sides of twoblank teeth are simultaneously formed irrespective of the number ofteeth on the blank, and in ettecting relative rotation between the hoband the blank.

Another object. of my invention is to proride a method of cutting ablank to form teeth having a straight profi-le that shall consist inproviding a hob having teeth arranged in the form of a thread, inso'positioning the hob and blank with respect to each other that the twosides of the blank teeth are simultaneously finished by different hobteeth. 4

A further object of my invention is to provide a method of the aboveindicated character for forming a sprocket wheel or a spline shaft from.a blank that shall consist in providing hob having teeth aring edgebeing located at the end of the hob, in positioning the hob with respectto the blank sothat the opposite sides of two blank teeth: aresimultaneously formed irrespective of the" number of teeth on the blank,and in effecting relative rotation between the hob and the blank.

Heretofore, it has been customary, with, very few exceptions, to hobvarious articles by means of a generating operation. In such case, eachof the various teeth on the hob serves to .form a portion of .the finalcontour of each tooth on the blank being out. However, in a form bob,the final contour of each tooth on the blank is not formed by a numberofhoh teeth. The last or final tooth on the hob may be set to out on aradial line of the blank and in such case the exact form of the lasthobtooth will be out on the blank. Hobs of the above indicated characterhave been made heretofore for shaping screw slotting cutters. \Vhen ahobis operated in such manner, one

I tooth on the -hob operates substantially in need to be, centered inthe same manner as -m1ll1ng cutters.

In a form hob constructed to be operated in accordance'with myinvention, a sprocket Wheel of the silent chain type or a spline shaftmay be bobbed with ease and efliciency. In my preferred constructionopposite sides of adjacent blank or sprocket tooth spaces aresimultaneously finished by cutting edges located on different hob teeth.By so constructing the hob with two finishing cutting edges located ondifi'erent teeth, it is possible to'hob sprocket wheels having variousnumbers of teeth if the pitch remains the same. Although my invention isparticularly directed to the bobbing of sprocket wheels and splineshafts, it is to be understood that my methods are equally applicable tobobbing other articles having ranged in the form of a thread and oneside of each two teeth has a formed finishing cutting edge. finishingedges is preferably located at the end of the hob. The side of the hobteeth carrying the finishing cutting edge intermediate the ends of thehob has two leads, the lead of said side is constant up to the finishingedge and then is changed so as to prevent cutting by the teeth beyondsuch finishing edge. Thelead on the opposite side of the hob teeth ismaintained uniform and may be the same as the lead of the teethfollowing the finishing edge on the side of the hob teeth having thefinishing cutting edge midway between the ends of the hob. The hobs usedin formi nga blank in accordance with .my invention are disclosed in myapplication Serial No. 609,941 filed December 30, 1922. It is to beunderstood that hobs constructed in accordance with my invention may bemade in accordance with any well known methods. Preferably, certainteeth of the hob are ground and especially the two finishing cuttingedges.

In the accompanying drawings:

Figure 1 is a diagrammatic view wherein one tooth on the hob carries thetwo finish ing cutting edges.

Fig. 2 is an end View of the hob shown in Fig. 1.

Fig. 3 is a plan view of the hob and blank shown in Fig. 1. I

Fig. 4 is a view similar to Fig; l'showing a sprocket wheel with alarger number of teeth.

Fig. 5 is a diagrammatic view illustrating a'hob having the twofinishing cutting edges located on different teeth.

Fig. 6 is a plan view of the hob and blank shown in Fig. 5.

Fig. 7 is a view'illustrating the hobbing of a spline shaft.

Fig. 8 is a developed view of the hob shown in Fig. 7.

Fig. 9 is an end view of Fig. 7. Y

Referring to the accompanying drawings and particularly to Figs. 1-, 2and 3, a hob 1. rotating on an axis my is shown in engagement with asprocket wheel blank 2. The blank is assumed to rotate on an axis mm.and comprises fourteen teeth 3 having straight sides 4 and 5. One of thesides 5 is shown making an angle a with a radial line on the .blank-Such angle a, it will be noted, varies with the number. of teeth on thesprocket wheel.

The action of form hobs in, cuttin a sprocket wheel or a splined shaftmay best be explained by considering the planing ac tion of a suitablerack in shaping a sprocket wheel or a spline shaft. The rack may beassumed to mesh with the sprocket wheel blank in the position shownoccupied by the the hob shown in The tooth carrying one of said ,tainedby considering points on the teeth of the wheel. The sprocket wheel 2 isassumed bob 1. The rack may. be considered to be a projection of a hob.

The pitch lines for a rack adapted to cut the teeth on the sprocketwheel may be obto be in a central position with a tooth space bisectedby a radial line CZ. A line' perpendicular to the side 4 of the tooth tothe right of the line CZ is drawn through a point L. .The point L isassumed to be located on the side 4 of the tooth under con siderationnear the top thereof. The line through the point L intersects the lineCZ at a point L. A line through the point L perpendicular to the line CZdetermines the pitch line for a rack which will out the side QL or 4: ofthe tooth shown to the right of the line CZ. During meshing between therack and the sprocket wheel, the pitch line through L rolls on a circlethrough L having a center located at C.

Assume the rack being considered to have a cutting edge 6 parallel tothe side LQ of a hob tooth and to be slowly moved along the pitch linethrough L while-the blank 2 is correspondingly rotated aboutthe centerC. If such movement between the rack and the blank is continued beyond apredetermined point the side 6 on the rack will finally generate aninvolute on the blank when the line 6 has been moved to the right of theline LQ as shown in Fig. 1 of the drawings. Thus,'the line LQ is thestarting point for the generating operation and up'to such position theline 6 shown four different positions of the cuting. side 6 of a racktooth while rolling on the circle through point L and having a center atC. In each of positions 6', 6" and 6 of the side 6 on a rack tooth, itisevident that the side Gcuts its own profile on a blanktooth. Moreover,it is'apparent that eachsubsequent position of the cutting edge 6completely cuts away the previous profile formed by the cutting edge. Inposition 6*? the cutting edge 6 coincides with the line LQ and cuts thecorrect pro file ontheblank tooth. If the cutting edge 6 were movedbeyond the position 6' an involute would be successively formed on theblank tooth. v

The above operation of the assumed rack is only true when the pitch lineof the rack passes through the point L and when the rack and the blankare considered as having relative rolling movement on such pitch line.If the pitch line is assumed to pass through the point L", a pointbeyond the point L on the line CZ, the cutting edge 6 will form aprofile similar to LQ on theblank tooth. However, theline LQ is not thelimiting position and the position when the forming of an involute 'isstarted. It is preferable in the case of a hob to use the pitch linewhere the line LQ, serves as a limiting position. A larger lead wouldcause the thickness of the hob teeth to decrease more towards the end ofthe hob.'

The opposite side NQ' of the tooth space under consideration may beformed by-the assumed rack in the manner similar to the forming of aside LQ by the rack. Through point'N at the base oft-he tooth a lineispasses through the point N perpendicular ly to the line CZ. A cuttingedge 7 which is assumed parallel to the line NQ, is moved toward theblank along the pitch line passing through the point N.

The cutting edge 7 will start to generate an involute when the line NC)is passed. Accordingly, the relative movement between the hob and therack is stopped'when the position NQ is reached in order that thecutting edge 7 will form its own contour similar to the line NQ on thetooth otthe blanlc The above statement is true for straight feed, perrevolution of the blank, which is equal to or smallerthan thecircumference of the circle having a radius UN. The same explanationwhich was given in explaining thecutting of the side QL of a blank toothis also applicable to the c utting of the side N Q of a tooth.

In place of considering the blank teeth to be formed with a rack bymeansof a planing process, such teeth may be considered to be formed by a hobwhich would mesh with the rack. The hob would have thickness of the hobteeth would vary as is indicated in Fig. 1 of the drawings. The.

two leads for the sides of the hobteeth would be constructed inaccordance with the ditferent pitches of the above considered rack. Itwill be noted that such a hob is used for bobbing sprocket wheels of thesilent chain type and that a ditferent hob must be provided it' thenumber of teeth on the sprocket wheel blankchanges. I

The bob 1 in Fig. 3 is shown set at an angle 6 with respect to the blank2. Al though such angle is usually made equal to the lead angle of thepitch circle, it in ay be varied and even made zero. The directionofmo'vement of the hob and blank are indicated by the arrows in Figs. 1,2 and 3 of the drawings. The difference between the pitch on the twosides of the hob teeth '2 and 3 of the drawings. The angle on between aside of a blank tooth and a radial line clearly shown in Fig. 41 of thedrawings to be larger than in Fig; 1 of the drawings.

Moreover, it is apparent-that the difference in lead between the twosides of the hob teeth can be maintained smaller the larger the numberof teeth to be formed on the sprocket wheel. The difference between thepitch on the two sides of the hob teeth is indicated by the lines a andb in Fig. 4 of the drawings. According to the above method, blankshaving different tooth numbers require different hobs.

Referring to Figs. 5 and 6 of the draw-- ings, a hob is illustratedwhich is adapted to formv teeth on various sprocket wheels irrespectiveof the number of teeth thereon if such sprocket wheels are adapted tooperate with-chains of the same pitch. In Fig. 5, it is apparent theangle 6 formed by the sides of the toothspaces or the angle 6' formed bythe two sides of a tooth change in accordance with the number of teethon However, when consldermg I the blank. sprocket wheels of the silentchain type, it is apparent the angle y which is formed by opposite sidesotadjacent tooth spaces remains unchanged irrespective of the number iof teeth on the blank.

It is evident the angle y must remain constant it the various sprocketwheels are to mesh with chains having the same size links therein, theangle 7 being the angle of the sides of the links. Thus, if a hob isprovided with teeth 'formed in accordance with the angle y and isadapted to finish adjacent sides of alternate blank teetheon the blank,one hob may be provided for bobbing sprocket wheels of various numbersof teethwhich are adapted .to operate with the same size chains. The finishing cut, which is indicated as being effected in Fig. 5 of thedrawings, is preferably performed in the symmetrical position of theblank.

A hob15 having teeth 16 is shown in engagement with a sprocketwheelblank 17. The hob rotates on an axis X Y and the blank '17. having acenter C, rotates on an axis M' N. The blank 17 is provided with teeth18, one of .which is symmetrically placed with respect to a radial lineC" The hob 15 is provided with two teeth 19 and 20 having formedfinishing edges which serve to finish the teeth on the blank. The

finishing cutting .edge'of the tooth 19 is I finishing cutting edge ofthe tooth 20 is adapted to finish one side of the cutting tooth to theleft of the-radial line CZ',

as shown in Fig. 5 of the drawings. The edge of'the tooth finished bythe hob tooth 19 is indicated by reference characters AB and the edge ofthe blank tooth which is i finished by the hob tooth 20 is indicated bythe reference characters DA.

The pitch lines for the hob 15 are determined in a manner similar to theobtaining of the pitch lines of the hob shown in Figs. 1, 2 and 3 of thedrawings. A line is drawn through the point B perpendicular to the lineAB and the intersection of such line with the radial line C'Z determinesthe -est number of teeth. In such cases, the positions AB andA'D will bethe limiting positions for forming a sprocket wheel of such number ofteeth and for a sprocket wheel having a larger number of teeth, the

limits will extend beyond the lines AB and A D.

A hob, such as illustrated in Figs. 5 and 6 of the drawings, is providedwith a some what larger lead on one side of the hob tooth, namely, theside'which carries the cutting edge adapted to finish the side AB of theblank tooth. Moreover, as shown, none of the hob teeth extend beyond theline AB. The other side of the hob teeth having the cutting edge whichforms the line A D on the blank teeth preferably has a smaller lead thanthe lead first mentioned. The lead last mentioned is maintained only upto the finishing cutting edge on the tooth 20. Be-

yond the tooth 20 the lead of the hob may be made larger and in fact thesame as the lead on the opposite side of the hob tooth. It is preferablenot to have a large difference in lead between the two sides of theteeth inasmuch as a large difference in the lead causes the thickness ofthe hob teeth to decrease somewhat rapidly.

Although hobs of the character shown in Figs. 5 and 6 may be formed in alathe, it is preferable to form such hobs in accordance with the methodsdisclosed in my application Serial No. 566,855 filed June 8,4922.

In Fig. 6 of the drawings, the hob isshown ,set at an angle 6, which isthe lead angle of "the pitch circle. However, the setting angle betweenthe blank and the hob may be varied and in fact the angle 6 may be madea composite outline.

equal to zero if so desired. It is well known that involute gear hobsmay be set at any desired angle with respect to the blank being cut andlikewise hobs of the above indicated type may be constructed to be setat any desiredangle with respect to the blank being cut. It is apparentthat a hob set square with respect to the blankbeing cut is more easilycentered than a hob set at an acute angle with respect to the blank.

Referring to Figs. 7, 8 and 9 of the drawings, a hob 30 is showninengagement with a spline shaft 31. The hob 30'is adapted to rotate onan axis w"'3 and the spline shaft 31 isadapted to rotate uponan axis C.The hob tooth 86 is shown in operative position in Fig. 7 of thedrawings and the position of the hob tooth 43 when moved to operativeposition is indicated by dotted lines in Fig. 7 of the drawings.

' The hob 30 is constructed somewhat in the manner of the hobillustrated in Figs. 5 and 6 and is provided withtwo finishing cuttingedges which .are located on different hob teeth. It may be said that thetwo sides of atooth space on a spline shaft are finished by differenthob teeth.

In case both sides of the last tooth on the hob carried finishingcutting edges, trouble would be experienced in cutting the bottom ofeach tooth space. Referring to Fig. 7 of the drawings, a hob tooth G isshown in position-on a radial line C-V for finishing two sides of ablank tooth space. The hob teeth in such case would necessarily beprovided with the top portion partlystraight and partly curved, asindicated by the tooth G in Fig. 7 of the drawings. The bottom portionof each tooth space on the blank can be generated only along the lineCV, and accordingly the curved portion of the/tooth space could begenerated by straight hob teeth only below the center line CV and afterthe cutting teeth had passed the center. In this regard it may be notedthe roughing teeth on the hob, one tooth G only of which is shown,- areassumed to extend above the center line of the blank in Fig. 7, of thedrawings. The lower portion H may be generated by the hob teeth Whereasthe upper portion H" must from necessity be cut with a formed cuttingedge on the hob teeth. Accordingly, it. is impossible to avoidconstructing the tops of the hob teeth without It is possible-to formthe two finishing cutting edges on the same tooth and provide more teethafter the finishing tooth. In other words, teeth may be provided whichcome into cutting action after the operation of the finishing tooth. Bysuch means, the

tops of the hob teeth may be kept substantially straight. However, themanufacture of a hob having a finishingtooth located intermediate theends thereof 'is somewhat lowing the finishing tooth would do little.

cutting.

By effecting finishing cuts with two sides of different hob teeth, it ispossible to equalizethe work between the various hob teeth and toprovide a hob which is comparatively simple in construction. A hob ofthe above indicated type is shown developed in Fig. 8 of the drawings.;In Fig. S-of the drawings, the two finishing cutting edges F and F areshown formed on the hob teeth 36 and 43. In this regard it may be notedthat the cutting tooth 36 having a finishing edge F" is shown inoperative position in Fig. 7 of the drawings. On the upper side of thehob teeth, as shown in Fig. 8 of'the drawings the lead changes at thetooth 36. Thus, the teeth 32, 33, 34 and 35 are provided with a leadsomewhat larger than on the teeth 36, 37,3 39, 40, 41, 42 and 43. Thus,the upper sides of the hob teeth are formed along two different helices.

The second finishing cutting edgeF is formed on the last cutting toothas shown in Fig. 8,0f the drawings. By so locating the second cuttingedge on the last hob tooth, it is possible to provide but a single leadon the lower side of the teeth. Such lead on the lower side of the.teeth is preferably made equal to the lead of the teeth 36 to 43,inclusive, on the upper side of the hob teeth. Accordingly, in the hobshown in Figs. 7, 8 and 9 of the drawings, it is possible to form thetwo cutting edges on different hob teeth and to have two different leadson only one side of the hob teeth. The two different leads-correspond tothe pitch of a rack which is equivalent to the hob and which would meshwith the spline shaft after the same had been cut. The pitch lines aredetermined in the manner set forth in discussing Figs. 5 and of thedrawings and also in discussing Figs. 1, 2,- 3 and 4 of the drawings.The pointsK and K on the radial le C-Z in Fig.7 of the drawings are poins which are determinedby drawing lines normal tothe sides of the splineshaft teeth. The pitch lines as heretofore explained are obtained bydrawing lines through the points K and K" perpendicular to the lineG--Z. 4

If a hob of this t pe is ground, preferably only the relief sur acesahead of and up to the finishing edges (F' and F in Fig. 8) are ground.The relief surfaces of the sides following a finishing cutting edge arepreferably left unground. Thus, the upper sides of the teeth 36, 37, 38,39, 40, 41, 42 and 43- would be left unground. Such side cuttingconsists in providing a hob having difi'eredges do no cutting whatever.They may therefore be taken back further than shown in the drawing, andparticularly so if the hob is to be ground. The helix of the upper sidesof the teeth 37, 38, 39, 40,41, 42 and 43 (Fig. 8)' intersects the helixconstructed by the upper sides-of the teeth 32, 33, 34, 35 and 36 aheadof Fwhich is another way of saying that the finishingedge F plrotrudesover the helix of the following teet It will be understood thatsuehchanges and modifications may be made in my invention as fall within thelimits of the appended claims, I

lVhat I claim is:

1. The method of cutting-a blank, which consists in providing a hobhaving formed cutting edges, in locating the hob and the blank withrespect to each other so that opposite sides of'adjacent tooth spacesare finished in the same angular position of the blank, and in rotatingthe hob and the blank with respect to each other.

2. The method of cutting a sprocket wheel, which consists in providing ahob having formed cutting edges, in locating the formed cutting edges onthe hob and the hob and the blank with respect to each other so that oneside of two sprocket teeth may ;be finished simultaneously independentof the number of teeth on the blank.

3. The method of cutting a blank, which consists in providing a hobhaving formed cutting edges, in locating the hob and the blank withrespect to each other so that the two sides of a blank tooth space arefinished in different angular postions of the blank, and in rotating thehob and the blank with respect to each other. i

' 4. The method of cutting a blank, which consists in providing a hobhaving two formed cutting edges located on different teeth, in locatingthe blank with respect to the hob so that the two sides of a blank toothspace-are finished in different angular positions of the blank, and inrotating the hob and the blank with respect to each other.

5. The method'of cut-ting a.,blank such as a sprocket wheel or a splineshaft, which consists in providing a hob having two formed nishingcutting edges, in locating the blan and hob relative to each otherv sothat the opposite sides of a blank tooth space are finished in differentpositions of the blank,.and in rotating the blank and the hob withrespect to each other.

6. The method of cutting a blank, which consists in providing a hobhaving formed cutting edges, in locating the blank and hob relative toeach other so that opposite sides of adjacent tooth spaces are finishedsimultaneously. and in rotating the hob and the blank with respect toeach other.

ent leads on the two sides of the teeth, and two formed cutting edges ondifferent hob teeth, in positioning the hob so that one of the formedcutting edges efi'ectsthe final cut on one side of the blank teeth, andin effecting relative, rotation between the hob and the blank.

. 8. The method of hobbing a sprocket .wheel blank, which consists inproviding a hob having two formed straight cutting edges on differenthob teeth, in positioning the hob relative to the blank so that the twoformed cuttingcdges simultaneously effect finishing cuts on two sprocketteeth, and in effecting relative rotation between the hob and the blank.

9. The method of hobbing a sprocket wheel, which consists in providing ahob having a different lead on the sides of the teeth, in positioningthe hob with respect to the blank so that two cutting edges on differenthob teeth simultaneously effect finishing cuts on different blank teeth,and in effecting relative rotation between the blank and the hob.

1.0. The method of. hobbing a sprocket wheel, which consists inproviding a hob having different leads on the two sides of the teeth, inpositioning the hob with respect to-the blank so that one side-of twoblank tooth spaces are simultaneously finished, and in effectingrelative rotation between the blank and the hob.

In testimony whereof, I hereto aflix my signature.

ERNEST WILDHABER.

